Manufacturers of gear parts and bevel gears are constantly looking for alternatives to traditional manufacturing processes. When choosing machine tools, maximizing flexibility has become a major consideration, because companies are reluctant to confine themselves to relatively small gear Market segments. Heller Maschinenfabrik GmbH, Germany, has developed a process that can significantly improve production efficiency through its sincere cooperation with Voith. Its pre-milling and gear milling processes can often be completed on a single machine tool.

It is noteworthy that gear milling has recently been included in the hot topic of some machine tool manufacturers. In fact, it is obvious that we can use our existing capabilities in five-axis machining to tap new applications beyond the traditional applications of machining centers. Heller is also committed to this. Heller, headquartered in Niltingen, Germany, has made another step forward in the application of five-axis technology following the launch of the new F Series in autumn 2009. Gear milling provides an opportunity to tap all the potential of the F series of five-axis machining centers and the verified MCH-C series, and to make full use of the capabilities of machine tools and various processing possibilities. Finally, Heller worked closely with Voith to develop new processes suitable for specific application areas. Both companies filed patent applications for the process, hoping to create a sensation in the industry.

While the traditional manufacturers in the gear market continue to focus on special machine tools and tools for gear processing, the manufacturing center manufacturers provide complete processing solutions for various applications and the use of special software to achieve gear modeling. This kind of processing is based on mathematical method, which allows the perfect groove to be generated by CAD/CAM process. According to the literature of gear technology, there is no comprehensive mathematical model, such as bevel gear teeth system. Therefore, each CAD model used in CAD/CAM process is an approximate model. Traditional gear cutting machine tools are based on specific machine tool structure and have corresponding kinematics characteristics. This kind of machine tool generates the corresponding tooth profile according to the set parameters input into the machine tool. Although similar to the hobbing process, Heller uses a completely different method: directly input the gear parameters specified on the drawing into the machine tool control panel. Then, the control panel uses the data to generate five-axis cutting paths suitable for rough and finish machining in real time. In this way, there is no need for mathematically accurate 3D geometric models. Instead, predefined gear data from drawings should be used. The measurement machine tool can input the report directly into the compensation data of the machine tool control panel for processing. Another major advantage of this method is that current tool data, such as tool wear, can be incorporated into the ongoing process in real time. Therefore, the accuracy is improved accordingly. In addition to inter-tooth processing, HELLER also provides pre-milling technology for semi-finished products. Thus, the complete pre-cutting of the outer and inner contours can be realized by the first clamping, and the milling of teeth can be carried out by the second clamping. In order to improve process control, a specially adapted NC program has been developed. In this way, the whole workpiece can be processed on a single machine tool.

Production efficiency increased by two times

When programming, other five-axis machining centers claim that their machining centers are also universal and suitable for gear milling. For example, the use of end mills can provide a high degree of flexibility. However, according to Dr. Hannes Zipse, Heller's business development manager, this approach is not particularly productive and efficient. "Our processing usually has a high chip removal rate in order to achieve the same results in gear milling. Therefore, we have worked closely with Sandvik Coleman to develop custom crown-milling cutters with indexable inserts, such as hob cutters. This plays an important role. Compared with the traditional processing methods, the production efficiency is increased by two times. This means that the wider the spacing between teeth, the higher the productivity can be obtained. "The level of production efficiency depends essentially on the static and dynamic stability of machine tools. According to Reinhold Siegler, Heller's director of technology development, this is one of the most important points: "Very compact clamping is a necessary condition. This means that in our solution, the tray chuck is very close to the upper edge of the tray to firmly clamp the gear or bevel gear. Other benefits include our exceptionally rugged spindles, highly rigid mechanical components, and the use of short cutters that are well suited to demanding roughing processes. This is another reason why we can achieve higher productivity in rough processing than in vertical processing.

Specializing in General Solutions

The new technology can undoubtedly provide efficient solutions for different sizes of workpieces (starting modulus is 4): smaller five-axis machining center model FP2000 is suitable for maximum 720mm diameter; larger model FP4000 is suitable for maximum 900mm diameter; model MCH-C with HSK100 spindle taper is suitable for maximum 1800mm diameter; the upcoming new machine tool series is suitable for maximum 3000mm diameter. Although tool changing is very time-consuming, it is still very efficient to use special machine tools for mass production of pinion gears. Therefore, Heller/Voith process does not directly target traditional contract gear manufacturers that produce fewer types of work pieces in batches. The solution is aimed at system suppliers, such as vehicle manufacturers, machine tool manufacturers or machine tool parts manufacturers who also use the machine to perform other processing tasks. Gear box manufacturers are also interested in this, and their products include complete assembly parts. This solution is especially suitable for large gears, because the machine tools and technology Heller provides are suitable for various processing tasks.